Adjustable camshafts for valve trains of internal combustion engines, with cam elements adjustable in their phase position relative to each other, allow the control of inlet valves and exhaust valves of the internal combustion engine with different timings, without the need for an inlet camshaft for the inlet valves and a separate exhaust camshaft for the exhaust valves. The shafts mounted in each other rotate about a common rotation axis in the cylinder head and can be adjusted in their relative phase position via a control element. The cam elements are held rotatably on the outside of the outer shaft, forming a slide bearing gap. Via a bolt, the cam elements are connected rotationally fixedly to the inner shaft, and to pass the bolts through the outer shaft, the outer shaft has corresponding bolt openings formed linearly in the peripheral direction.
For example, DE 10 2009 012 143 A1 discloses an adjustable camshaft for the valve drive of an internal combustion engine, with an outer shaft and an inner shaft running concentrically and held rotatably in the outer shaft. Bearing sleeves are pressed onto the outside of the outer shaft and serve to hold the cam elements rotatably, and at the same time ensure the rotatable bearing of the camshaft in the cylinder head. For this, the bearing sleeves have a corresponding length and must be pushed onto the outside of the outer shaft. To arrange the cam elements on the bearing sleeves, these must first be extensively reworked, in particular to remove machining residue from the outer face of the bearing sleeves. The bearing sleeves are configured substantially wider for the common mounting of the cam elements on the bearing sleeves and for mounting the camshaft in the cylinder head, and the bearing sleeves must be machined over a great axial length. Furthermore, the disadvantage results that the bearing sleeves entail an increase in the slide bearing diameter on which the cam elements are mounted rotatably on the outside of the camshaft, unnecessarily increasing the friction occurring in the slide bearing arrangement.